Control mechanism



March 13, 1934. c. E. MAsoN 1,950,989

CONTROL MECHANISM Filed Aug. 14. 1928 Inveanom: .5 7 L'easowEZMason,

V Patented Mar. 13, 1934 .UNITED STATES CONTROL MECHANISM Clesson E.Mason,

Tulsa,'0kla., assignor to The Foxboo Company, Foxboro, Mase., acoi-noration of Massachusetts Application August 14, 1928, Serial No.%9,566 12 Claims. (CI. 236-82) This invention relates to controlmechanism adapted to control the supply of fluid to apressure-fiuid-driven servomotor Operating some mechanism, usually avalve in which case the s servomotor usually takes the form of adiaphragm motor, and the object is to provide a mechanism having aninitial rapid response to a governing action and slow responsethei-&after until the limit of response is reached. otherwise described,the invention provides in a sluggishacting mechanism means for effectingan initial rapid movement of the device controlled.

The specific embodiment of the invention disclosed by way of exampleherein is a Construction which emhodies features disclosed and claimedin a co-pending application of Webster W. F'rymoyer, Serial No 299,!57Z,filed Aug. lt, 1928, and in a sense may be considered an. improvement onthe mechanism disclosed in that application adapting it tor uses inwhich the mamer of operation above described is desi'able.

The accompanying drawing, to which reference is made in the followingdetailed description, is a diagrammatic disclosure of said specificembodiment of the inventlou as applied to a heat ing controlinstallation with parts in section.

To facilitate understanding of the invention, there will first bedescribed' specifically those parts of the installation which are shownand iully described in the Frynoyer application referred to, but it willbe understod that the construction thus described is iliustrative merelyand the detailed description has for its purpose making understood thatspecific mechanism heroin disclosed in connection with which the presentinvention is used and that the scopo oi the invention is not limited tothe application shown or the mechanism illustrated.

Reierring to the drawing, there is there shown a chamber 3 to whichheating fluid is supplied through a pipe 5 under control of the valve 'Iactuated by a diaphragm motor 9. In the chamber may be disposed a bulbll of a vapor pressure thermometer embodying a helical Bourdon tube 13which is adapted to operate a valve or flapper" 15 closing against thevalve seat or "nozzle" 17 constituting an exhaust port for a pressuresystem as will presently be described. This thermometer constitutes anexample of a mechanism adapted to -operate a control valve in accordancewith the fluctuations of a variable, ordinarily one the value of whichis dependent in part on the operation oi the valve 7 or similarmechanism. The flapper 15 is herein shown as directly attached to thehelical tube 13 and the nozzle 17 as stationary, but in practice theconstruction may Conveniently be similar to that disclosed in the patentto Dixon 1,582,868. April 27 1926.

To operate the diaphragm motor, fluid under ao pressure is supplied froma suitable source through the pipe 19, through the control head 21 andpipe 23 to the chamber of the diaphragm motor. The chamber 25 in thecontrol head from which the pipe 23 is supplied may have 35 in one wallthereof an intake port 27, and in alignment therewith an opening 29.Supported exteriorly of the opening and in communication with chamher 25through the same is a set of expansible diaphragms 31, and the oppositewall 'm of the chamber formed thereby, which moves when the chamberexpands under pressure, is provided with an exhaust port 33. Cooperatingwith these pcrts is a suitable double valve embodyirg a valve stern 3-1having heads 35 and 37 m i adapted to close the intalte and exhaustporte respectively and being spaced &part cn the stern a distanceslightly less than the normal distance between these porte. .h spring 39normally presses the valve to the right and the supply' go port isclosed but the waste or exhaust port is open, the seat of the head. 37being supported by the diaphragms 31 away from that head. This doublevalve serves as an example of a supply and waste valve and in theposition shown 35 pressure fluid from pipe 19 is cut off from thediaph'agn motor and the chamber of the diaphragm motor is exhausted tothe atmosphere through the open waste port at 33.

To permit pressure fluid to flow todiaphragm motor 9 the supply andwaste valve may be operated by a pressure operated motor which hereintakes the form of an expansible diaphragm il opposing the diaphragms 31and adapted when dilatecl to make contact with the ported wall of thelatter, compressing diaphragms 31, moving the seat of the waste valveagainst head 37 and closing port 33 and then by bodily movement of valvestern 34 with its attached valve heads opening the supply valve againstthe spring 39. To expand diaphragm 41 air may be admitted from the mainsource of supply, through pipe 43, in which is located the exhaust portprovided by the nozzle 17, through a restricted connection 45 adapted topermit only a slow seepage of pressure fluid therethrough and which inthe example illustrated takes the form of a length of capillary tubing,and through pipe 47.

The mechanism as so far described is as disclosed in said Frymoyerapplication and provides for a floating controlled valve 7 having 'asluggish response to the governing 'movements of control valve 15, aswill be understood from the following description. Air under suitablepressure, say flfteen pounds per square inch is admitted at pipe 19. Letus suppose valve 7 to be held partly open by a pressure of ten pounds inthe diaphragm' motor 9. The same pressure will' phragm'motor 9 anddiaphragms 31 falls, diaphragm 41 expanding will further compressdiaphragms 31, closing waste valve 37 and opening supply valve wider.Now, if the temperature 'in the chamber 3 increases, the thermometerwill move flapper 15 away from nozzle 17, exhausting pipe 43. Pressurefluid will slowly seep through connection 45, diaphragm 41 will slowlycollapse permitting diaphragms 31 to expand, supply valve the pressurein diaphragm motor 9 and moving controlled valve 7 towards closedposition to reduce the supply of heating medium.

. and the diaphragm 41. In embodying my invention in a construction ofthis type I provide for means independent of the restricted connection'whereby the change on the intake side effects a quick initial change onthe dischar'ge side with a corresponding quick movement of controlledvalve 7 to be followed, if necessary, by a slow change to the finalpressure called for by .the control.

To obtain this effect I place in communication with the pressure systemof the diaphragm 41 on either side of the connection 45 by means ofbranch pipes tapped off from either side thereof expansible chambers 49and 51 which may take the form of bellows or sets of diaphragms, eachsupported at one end on a frame 55 and having the movable walls at theiropposite ends facing each other and rigidly connected by a member 57 insuch manner that the expansion of one compresses the other. I haveherein-shown the member` 57 as threaded and carrying the nuts and locknuts 59 adjustable therealong and adapted to cooperate with an arm 61carried by the frame to limit the movement of the diaphragms in onedirection or another in an amount controlled by the position of thesenuts along the thread.

The operation is as follows. Assume that the flapper valve 15 closesexhaust port 17 and the pressure rapidly rises in pipe 43 to betransmitted only slowly through the restricted connection 45. Theincreased pressure, however, is quickly felt in diaphragm 51 whichexpands, collapsing diaphragm 49 and reducing the volume of the systemon the discharge side of the connection 45 and consequently causing aquick increase in pressure therein which is felt in the diaphragm 41,and causes a quick response of the control mechanism. This pumpingmovement of the diaphragms is halted by the left-hand stop 59 and theVolume of chamber 49 is now for all practical pn'poses fixed. Pressureseeping through the connection 45 continues to build up in the chamber41 providing a sluggish response of the mechanism following the initialrapid response until the desired conditions are obtained.

Now, if we suppose that the control valve 7 has opened so wide that theindications of the instruments are higher than the control point,control valve 15 will open, rapidly exhausting pipe 43 and diaphragm 51,the pressure in which is then overbalanced by the pressure in 49 so thatthe latter expands, compressing the former and causing a sudden drop inpressure on the discharge side of the system and in chamber 41 providinga rapid initial response of the mechanism to be followed by a slowerresponse due to seepage of fluid through connection 45.

I am aware that the invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof, and Itherefore desire the present embodiment to be considered in all respectsas illustrative and not restrictive; reference being had to the appendedclaims rather than to the foregoing description to indicate the scope ofthe invention.

I claim:

1. A pneumatic control mechanism comprislng 35 to close and waste valve37 to open, reducin wa pres ure Operated motor for Op r ting valvesgoverning the supply of pressure fluid to the controlled mechanism, acontrol valve governing the supply of fluid to said motor, a restrictedconnection between said valve and motor, and chambers of variablecapacity in communication with the system at either side of saidconnection A and so connected that change in Volume of one will changethe Volume of the other in opposite sense;

2. A pneumatic control mechanism comprising an expansible chamberserving as a motor for Operating valves governing the supply of pressurefluid to the controlled mechanism, means including a control valve forcausing a slow flow of pressure fluid to and from said chamber, andpumping means' also gover'ned by said control valve to efiect arelatively rapid change in' pressure conditions in said chamber onoperation of said valve. I

3. A pneumatic control mechanism comprising an expansible chamberserving as a motor for Operating valves governing the supply of pressurefluid to the controlled mechanism, a control valve gcverning flow ofpressure fluid to and from said chamber, a restricted connection betweensaid valve and chamber, dilatable chambers in communication with thesystem on either side of said connection and acting one on the other inopposition, and stop means to limit the corresponding dilation of onechamber and diminution in Volume of the other.

4. A penumatic control mechanism comprislng a supply and waste valve,means responsive to the controlled pressure tending to Shift the valveto waste position, a pressure responsive device for shifting-the valveto supply position in opposition to said means, means to control theflow of pressure fluid to and from said device comprising a controlvalve responsive to the fluctuations of a variable, a connection ofminute capacity between said control valve and said device, and meansactuated by the change in pressure on the intake side of said connectiondue to the operation of said valve to eflfect an initial change in thepressure conditions on the discharge side independently of'flow throughsaid connection.

5. A pneumatic control mechanism comprlsing a supply and waste valve,means responsive to the controlled pressure tending to Shift the valveIIO to waste position, a pressure responsive device !or shiiting thevalve to suppiy position in opposition to said means, means to controlthe flow of pressure fluid to and iron said device comprising a controlvalve responsive to the fluctuations oi a variable. a connection ofminute capacity between said control valve and said device, andexpensible and contractible chambers in communication with the system atopposite sides of said connection mutually connected whereby a change involume oi one effects a change in Volume of the other in opposite sense.

6. In combination with a mechanism actuated by-a pressure operatedmotor, a control valve responsive to the fluctuations of a variable thevalue oi' which is dependent on the adjustment o! said mechanism, meansincluding a sluggishly acting connection to render the pressureconditions set up by actuation of said valve eflective to cause a slowvariation in the pressure admitted to the motor tending to adjust saidmechanism in manner to cause a change in said variable opposite in signto that causing such movement of the control valve, and cooperatingmeans operated on actuatin o! said valve to eflect an initial rapidchange in the pressure admitted to the motor independent o! saidsluggishly acting connection.

7. A control mechanism for a pressure fluid operated motor comprising avalve !or controlling the supply of pressure fluid to said motor,pneumatic means tor governing the same comprising a control valve, meansincluding a sluggishly acting connection to render the pressureconditions set up by actuation oi said control valve effective to causea slow adjustment of said first valve, and cooperating means operated onactuation o! said control valve to eflect an initial rapid adjustmentoi' said' flrst valve independent ofsaid sluggishly acting connection.

. 8. A pneumatic control mechanism comprising a supply and waste valve,a pressure operated device to Shift the valve towards one position andon exhaust permitting its return towards the other position, a controlcouple governing the supply of pressure fluid to said device andmechanism operated thereby to move rapidly a considerable volume otfluid to or rrom said device and cooperating mechanism permitting asubsequent continued slow flow in the same direction.

9. In combination with pressure operated motor mechanism tor controllingthe flow oi a fluid. means responsive to a measurable condition airectedby such flow, means to supply on a predetermined response of said meansto said valve in initial relatively rapid and powertul impulse and asecondary slower impulse comprising a supply and waste valve throughwhich pressure fluid is supplied to the motor mechanisni, a pressureoperated device !or moving the .a continued gradual flow.

10. In combination with pressure operated motor mechanism forcontrolling the flow of a fluid, means responsive to a measurablecondition affected by such flow, means to supply on a predeterminedresponse of said means to said valve mechanism an initial relativelyrapid and powertui impulse and a secondary slower impulse comprising asupply and waste valve through which pressure fluid is supplied to themotor mechanism, a pressure operated device for moving the same, acontrol couple actuated by said responsive means goveming the supply offluid to said device, means to transmit through said supply valve to thevalve mechanism a rapid flow o! fluid to said valve mechanism onoperation of said couple, and cooperating means comprising a restrictedseepage passage and a chamber oi' relatively great Volume incommunication therewith at the discharge side thereot for the pressurefluid to provide a continued gradual flow. I

11. In combination with valve means for controlling the flow of a fluid,pressure operated motor means for moving the same and means to convey tosaid motor means a relatively rapid flow of pressure fluid to cause arapid response and an initial marked change of the controlled flow and afollowing slow flow ot pressure fluid to cause a sluggish change in therate oi flow comprising a control couple Operating to initiate a flow ofpressure fluid, means freely receiving such flow to transmit itspressure substantially undiminished I and a second cooperating passagefor said fluid comprising a restricted portion through which it seeps.

12.' In combination with valve means !or controliing the flow ot afluid, pressure operated motor means for moving the same and means to 1convey to said motor means'a relatively rapid flow of pressure fluid tocause a rapid response and an initial marked change of the controlledflow and a following slow flow o! pressure fluid to cause a sluggishchange in the rate of flow comprising side thereot.

' CLESSON E. MABON.

